This invention relates to superconducting windings in general and more particularly to a support structure for transmitting the large forces generated in such a winding.
A support structure for transmitting large forces between a superconducting magnet winding cooled to a very low temperature and an abutment body which is at a higher temperature level and takes up the forces, utilizing support elements which point at least approximately in the direction of the force transmission and between which stiffening elements are attached, and having at least one heat shield extending over an area is described in U.S. Pat. No. 3,980,981. Such support structures are required particularly for inductive, superconducting storage devices. The great advantage of such storage devices is seen in the fact that with them, energies on the order of magnitude of 10.sup.12 joule or more can be stored in a relatively small volume, energy densities of about 10 joule/cm.sup.3 being obtained with magnetic flux densities of about 5 Tesla. Flux densities of such magnitude can be achieved economically in magnet windings only by means of so-called technical Type-II superconductors such as niobium-titanium (Nb--Ti), niobium-tin (Ni.sub.3 Sn) or vanadium gallium (V.sub.3 Ga). Such storage devices generally contain a number of coaxial solenoids of these conductors, into which the electric energy is fed during low load periods of many hours via inverters from a connected network. At peak load times, the required energy can then be given off again to the network over a period of minutes or hours.
According to one proposal for such a superconducting energy storage device, with which several gigawatt-hours can supposedly be stored, three magnet windings are provided, each of which has a diameter of between 120 and 150 m, is 4 to 5 m wide and 8 to 10 m high. These windings are to be fabricated in situ in tunnels which are driven into the rock ("IEEE Transactions on Magnetics", Vol.MAG-11, No. 2, March 1975, pages 475 to 488).
The forces emanating from the superconducting winding of a magnetic gigawatt storage device such as Lorentz forces can be in the order of 10.sup.11 Newton. It must be possible to transmit these very large forces safely by a support structure between the superconducting magnet winding and an outer abutment which takes up the forces and for which, especially for cost reasons, natural rock is provided. In addition, a prime requirement for a support structure suitable for this purpose is that the terminal losses caused by it due to heat influx through a solid body must be kept as low as possible, since the economic feasibility of a superconducting energy storage device is determined, in particular, also by these heat losses.
These requirements are supposedly also met by the support structure described in U.S. Pat. No. 3,980,981. According to one embodiment, this support structure contains columnar support elements which extend radially outward with respect to the axis of the superconducting magnet winding approximately in the direction of the force transmission. These support elements are furthermore mutually guyed by wires to provide a sufficiently strong support structure. (FIG. 1) Also, pairs of support elements can have their ends facing the magnet winding engaging a common support point, so that they represent the two legs of an A-shaped support arrangement. The support elements of such a support arrangement are furthermore held in a firm mutual position by stiffening elements extending transversely to the bracing direction. (FIG. 3) In addition, thermal radiation shields which extend as surfaces approximately concentrically about the magnet winding and consist of metallic surfaces and superinsulation, are provided in the known support structures.
It was found, however, that these known support structures, even those with A-shaped supports, have only relatively low buckling strength. In order to prevent buckling of the supports under load, the supports of the known support structure must then have a sufficiently large material cross section. This, however, leads to correspondingly large losses due to heat inflow to the parts of the storage device which are cooled to the lowest temperature.
It is therefore an object of the present invention to design a support structure of the kind mentioned at the outset in such a manner that the large forces occurring in a superconducting energy storage device can be transmitted safely by it and the heat losses due to solid body heat inflow via the support cross section are nevertheless relatively small.